Pages

This week marks the start of the annual eat-too-much and
move-too-little holiday season, with its attendant declining health and
surging regrets. But a well-timed new study suggests that a daily bout
of exercise should erase or lessen many of the injurious effects, even
if you otherwise lounge all day on the couch and load up on pie.
To undertake this valuable experiment, which was published online in The Journal of Physiology,
scientists at the University of Bath in England rounded up a group of
26 healthy young men. All exercised regularly. None were obese. Baseline
health assessments, including biopsies of fat tissue, confirmed that
each had normal metabolisms and blood sugar control, with no symptoms of
incipient diabetes.
The scientists then asked their volunteers to impair their laudable health by doing a lot of sitting and gorging themselves.
Energy surplus is the technical name for those occasions when people
consume more energy, in the form of calories, than they burn. If
unchecked, energy surplus contributes, as we all know, to a variety of
poor health outcomes, including insulin resistance — often the first
step toward diabetes — and other metabolic problems.
Overeating and inactivity can each, on its own, produce an energy
surplus. Together, their ill effects are exacerbated, often in a very
short period of time. Earlier studies have found that even a few days of
inactivity and overeating spark detrimental changes in previously
healthy bodies.
Some of these experiments have also concluded that exercise blunts
the ill effects of these behaviors, in large part, it has been assumed,
by reducing the energy surplus. It burns some of the excess calories.
But a few scientists have suspected that exercise might do more; it
might have physiological effects that extend beyond just incinerating
surplus energy.
To test that possibility, of course, it would be necessary to
maintain an energy surplus, even with exercise. So that is what the
University of Bath researchers decided to do.
Their method was simple. They randomly divided their volunteers into
two groups, one of which was assigned to run every day at a moderately
intense pace on a treadmill for 45 minutes. The other group did not
exercise.
Meanwhile, the men in both groups were told to generally stop moving
so much, decreasing the number of steps that they took each day from
more than 10,000 on average to fewer than 4,000, as gauged by
pedometers. The exercising group’s treadmill workouts were not included
in their step counts. Except when they were running, they were as
inactive as the other group.
Both groups also were directed to start substantially overeating. The
group that was not exercising increased their daily caloric intake by
50 percent, compared with what it had been before, while the exercising
group consumed almost 75 percent more calories than previously, with the
additional 25 percent replacing the energy burned during training.
Over all, the two groups’ net daily energy surplus was the same.
The experiment continued for seven days. Then both groups returned to
the lab for additional testing, including new insulin measurements and
another biopsy of fat tissue.
The results were striking. After only a week, the young men who had
not exercised displayed a significant and unhealthy decline in their
blood sugar control, and, equally worrying, their biopsied fat cells
seemed to have developed a malicious streak. Those cells, examined using
sophisticated genetic testing techniques, were now overexpressing
various genes that may contribute to unhealthy metabolic changes and
underexpressing other genes potentially important for a well-functioning
metabolism.
But the volunteers who had exercised once a day, despite comparable
energy surpluses, were not similarly afflicted. Their blood sugar
control remained robust, and their fat cells exhibited far fewer of the
potentially undesirable alterations in gene expression than among the
sedentary men.
“Exercise seemed to completely cancel out many of the changes induced
by overfeeding and reduced activity,” said Dylan Thompson, a professor
of health sciences at the University of Bath and senior author of the
study. And where it did not countermand the impacts, he continued, it
“softened” them, leaving the exercise group “better off than the
nonexercise group,” despite engaging in equivalently insalubrious
behavior.
From a scientific standpoint, this finding intimates that the
metabolic effects of overeating and inactivity are multifaceted, Dr.
Thompson said, with an energy surplus sparking genetic as well as other
physiological changes. But just how exercise countermands those effects
is impossible to say based on the new experiment, he added. Differences
in how each group’s metabolism utilized fats and carbohydrates could
play a role, he said, as could the release of certain molecules from
exercising muscles, which only occurred among the men who ran.
Of more pressing interest, though, is the study’s practical message
that “if you are facing a period of overconsumption and inactivity” —
also known as the holidays — “a daily bout of exercise will prevent many
of the negative changes, at least in the short term,” Dr. Thompson
said. Of course, his study involved young, fit men and a relatively
prolonged period of exercise. But the findings likely apply, he said, to
other groups, like older adults and women, and perhaps to lesser
amounts of training. That’s a possibility worth embracing as the pie
servings accumulate.